High-voltage fuse



ET AL Jan. 25, 1955 R. L. MURRAY m 0 E MN m R R M 4 E m w l o w w m W EW m I 5 U M l .1 m $1 6 W E m U/ m C L R m m u w M R W D K E 2 m 6 l/ VH A //////l O w fl/ W D x 6 m 7 a m J m w United States Patcnt-OfliceRe. 23,930 Reiuued Jarn25, 1955 23,930 HIGH-VOLTAGE FUSE Ro ceL..Murray, William H. McClure, and Edgar W.

n, In, Birmingham, Ala., rs to USCO Power Equipment Corp., Birmingham,Ala a corporation of Alabama Original No. 2,660,644, dated November 24,1953, Serial No. 235,996, July 10, 1951. Application for rem September10, 1954, Serial No. 455,373

3 Claims. (Cl. 200-431) Matter enclosed in heavy brackets [II appears inthe original patent but forms no part of this reissue specification;matter printed in italics indicates the additions made by reissue.

This invention relates to electrical fuse devices for use in highvoltage power distribution systems, and more particularly toimprovements in tubular power fuses in which a fuse link is formed ofasmall diameter fusible conductive element which joins relatively largerconductors electrically connected to spaced fuse end terminals, andextends coaxially through an insulator tube or sleeve mounted betweenthe end terminals as a protective casing. The drop out fuse devicedlsclosed in United States Patent No. 2,365,113, issued December 12,1944, to W. O. Schultz is one form of such priorart device while anotherform of such a fuse device is that shown in United States Letters PatentNo. 2,485,221, issued October 18, 1949, to F. H. Turnham et al.

In such fuse devices, much difficulty has been encountered in the pastas a result of disintegration of the fuse link and the arc extinguishinggas producing liner caused by the corona effect produced around thesmall diameter wire in high voltage installations. This difficultyresults from the fact that the corona produced around the fusible wireacts on the constituents of the surrounding air in the tubular insulatorto break down the oxygen to form ozone (a), a portion of which thenchemically combines with the nitrogen component and water vapor to formnitrous acid. The nitrous acid thus formed collects on the fusible wireand the liner and produces corrosion or an eating away of I the smallfusible wire and liner. Since the diameter of the fusible wire is afunction of the maximum current carrying capacity for which the fuse isdesigned, resort cannot be made to the obvious procedure of enlargingthe diameter of the conductor to eliminate the corona effect.

Since this corrosion of the fusible wire and disintegration of the linerresults respectively in a reduced current carrying capacity or currentrating of the fusible element and excessive burning of the liner uponfusing of the fuse link it has been found necessary in practice tofrequently inspect high voltage fuse installations and replace the fuselinks of such fuse devices at from three to six month intervals and toreplace the tubes themselves when disintegration of the liner hasprogressed sufliciently regardless of whether the current load hasexceeded the current rating of the fuse. Since the fuse link of fusedevices of this type heretofore provided must be frequently replaced,much inconvenience and a high cost of maintenance of the powerdistribution system results. This has limited the fields of applicationof these otherwise highly satisfactory and relatively inexpensive fusedevices.

To avoid possible ambiguity and to more clearly state the object andpurpose of this invention, the meaning of the word corona," as known andused by those familiar with the art of electric pbwer generation andtransmission, is the electric overstressing or ionization of the layerof air in contact with a conductor.

Further, since the object and purpose of this disclosure is to controland prevent corona formation and its consequent damage to [an] essential[element] elements of electric highvoltage fuses, we will point out theprincipal physical law which governs the formation of corona. Since theelectric gradient in air surcompensate for or 1 rounding an electrifiedconductor increases as the distanee from the conductor is decreased inmuch the same relation as light intensity increases as the distance tothe source is decreased, it follows that for a-given conductor radiusthere is a voltage level above which the surrounding air cannotwithstand the voltage stress and the conductor is enveloped in a layerof minute radially extending sparks or electrically punctured air,tending to build or extend the conducting surface to a radius largeenough that the air boundary will withstand the electric stress.

As is well known, the melting point of a fusible wire is fixed by thewire size, and for practical ratings the wire size is small compared tothe size necessary to be above the critical size for corona-freeoperation on high voltage, the priricipleIIs] of which was described ave.

With the above principles and facts in mind, this disclosure describesways and means to surround the fuse wire which is excessively small withregard to being corona-free with a sufliciently conducting surface ofcorona-free radius operating at near the same voltage as the fuse wire,at the same time being of vsufficiently high resistance to not in anyway impair the operating functions of the fuse structure.

The prime purpose of this invention is to effectively enlarge the radiusof the corona forming element without. enlarging the fusible element andwithout adversely affecting the function and operation of the fuse.

Since the current required at commercial frequency to charge the surfaceof a conductor in space is a small value compared to the current ratingof the fuse, it becomes feasible to provide a concentric electrifiedsurface over the fuse and having a radius sufficiently large to be freeof corona at the rated voltage at the same time being in the form of ahigh resistance end to end so as not to interfere with the currentinterrupting properties of the assembly and subsequent insulating periodafter the fuse operates.

it is, accordingly, a primary object of this invention to provide arelatively inexpensive tubular power fuse of an improved constructionwhich assures long life of the fuse link and gas producing liner evenwhen utilized for high voltage installations and avoids the necessity offrequent inspection and replacement of the fuse link thereof.

It is a further object of this invention to provide arelativelyinexpensive high voltage fuse of an improved construction inwhich the corrosion resulting from the corona effect heretofore producedaround the small fusible element is substantially eliminated.

More specifically it is an object of this invention to grovide a tubularfuse comprising a fuse link shielded y a resistor element of highresistance value connected electrically in parallel therewith so thatthe corona heretofore developed around the fusible element thereof issubstantially eliminated.

A further object of this invention is to provide a tube or sleeve for atubular fuse assembly which is of an improved construction adapted tosubstantially eliminate the corona effect heretofore produced around thefusible element thereby obviating the corrosion normally encountered inuse of such fuses on high voltage lines.

A further specific object of this invention is to provide an insulatingtube or sleeve adapted to extend between [space] spaced end terminals ofa fuse device in surrounding relation with the fuse link thereof with anintegral cylindrical resistor of high resistance value coextensive inlength therewith.

More specifically, it is an object of this invention to provide a fuselink tube having a resistive coating cm extensive in length with thetube formed'intermediate two of the layers of insulating materialthereofand electrically connected to the terminal ferrules used toconnect the fuse in the line.

These and other objects of this invention will become apparent from thedetailed description and appended claims when read with reference to theaccompanying drawing wherein:

Figure l is an elevational view of one form of a single tube fuseassembly, to which the present invention is particularly applicable;

v 3 Piul'eZisanenlaggedfiewofthehinge-andkrminal assemblyatoneendthefusedeviceof F lwhich "maciserveas the hinge end ofamoditiedorm'offuse as shown in the aforementioned Turnham et a]; ten' Pig lu'e 3is an enlarged view of the latching end termi- F '1; an

igure 4 is a sectional view of the sleeve or tube surml big at theopposite end of the fuse device of roundin the fuse link takensubstantiallyalong the line 10 4-4 of igure 3.

The illustrated form of fuse device, shown in its closed 4 fiolskitionin Figure l of the=drawin comprises 'a fuse 10 surrounded by a tube oreeve 12 electrically and mechanically connected throu pivoting in acounterclockwise direction about the axis of pivot shaft 22 of endterminal assembly 14 to its open ggsition. This eifects acompleteelectrical disconnection tween the end terminalassemblies. 1 Thestructure of end terminal assembly and associated in the above mentionedUnited States Letters Patent No. 2,485,221. The end of the fuse linktube 12 is mounted in aperture 24 formed in a hinge casting 26. and issccured thereto by suitable means not shown. The corresponding end ofthe fuse link 10 extends from theend 3 of tube 12 around an arm 28formed integral with the, casting 26 and -is secured in electricalcontact with 'talie ca ting 26 by a suitable machine screw '30 and plate'l'hecasting26issecuredtoasupportorhingearm which is pivotally mountedonthe shaft 2: and which 40 is spring biased in a counterclockwisedirection about the shaft 22 bya suitable torsion spring not shown. .The

arm 34 is normally held in the position shown in Figures 1 and 2 againstthe force exerted by the torsion spring by the eng'agementof a air ofcoacting latch'tnembers 36 and 38, the former ing pivotally mounted at,

. upon the casting 26 and the latter being pivotally mounted upon thebase plate. 42 of the end terminal assembly 15.. A m'embe 46, atorsion-spring (not shown) being provided to nor mally bias ejector 44in" a'clockwise direction about the pivot 46 from-the position shown.Eiector 44 is formed with an armi48havina a bifurcated end'providing'a'n aperture 49 through which the fuse link 1. extends and atone side with an ear 5. having a pin52 fixed thereon and engaged in the.slot of the bifurcated upper end of latch member 36.

the slot of the bifurcated end of. the latch meinber 36 causes the latchmember 36 to pivot in a counterclock wise direction about the pivot 40upon disengagement of 79 latch 36 from the latch 38, the arm. thecasting 26 and the fuse link tube 12 pivot in a counterclockwisedirection under the force of the torsion spring about the shaft 22. Ashock absorbing mechanism such as shown in PatentNo. 2,485,221 ispreferably provided to arrest movement of this assembly at the end ofits stroke.

Coacting contact members 54 and 56, which are secured respectively tothe casting 26 and the base 42. establish an electrical connection fromthe base plate 42 to the casting 26 and end of the fuse link 10 which issecured thereto so long as the assembly is in its latched position.

If further explanation in mechanical arrangement of this end terminalassemblv 14 is found to be necessary for a complete understanding of thepresent invention. refer-, ence is made to the aforesaid Turnham et al.patent.

terminal ferrules 13 5 and 14 to spaced terminal assem lies 15 and '16.]Terminal assemblies 15 and 16 are conventionally mounted from the line20 upon occurrence of an, overload through'mechanical sepabout shaft 22to its open '-Thisisawellknown n44, known as a fuse linkejecton'is oiv--otally mounted upon the casting extension or car 28 at 50 Uponoccurrence of an overload causin the I 4 Theend terminal assembly 16 andassociated terminal fcrnile 14, which is also of a releasable latchconstructi isshown inanenlarged' view'inFigure 3. Anend ckng'flt havingan aperture 62 through which the sleeve 5 12 extends is secured theretobyia set screw 64. The associatedend of the fuse link 10 extends fromthe end The fuse tube is latched in the position shown in Figure 1 bythe coaction of latches 0 and 72, the former beingplvotally mounted uponthe casting 60 at 74 and thetlat'tzr pivotallymounted upon the terminalbase p a e at Release of latch 76 from latch 72. is effected upon fusionof fuse link 1. simultaneously with the disengaglc Y ment of the latchesof theopposite end terminal assem by a suntlar release linkage. Anejector 80, which is spring biased in a [counterlockwise]counterclockwise .direction about its pivot 82 on casting 60, is held inthe silica shown by fuse link 10 which passes through its l o pertured]apertured lower end. Upon severance of the fuse link 10, the springurged counterclockwise movement of e tor produces clockwise movement oflatch member 0 to its disengaged ition through the coaction of pin 84,fixed to ejector la with the slot of the bifure cated upper end of latchmember 70.

In this fuse assembly'structure severance of thefuse link upon theoccurrence of an overload will simultaneterminal, ferrule'lS is shown inFigure 2 in .detail and is quite similar to thatdisclosed and describedin detail 30 ously effect they release of the latches of both endterminal assemblies to permit counterclockwise movement of the fuse tube12 and the associated elements thereon ition. As is best illustrated inFigure 2, the fuse! 10 comprises twopieces of flexible copper conductorand 92 to the adjacent ends of which are soldered two smaller conductors94 and 96 respectively. The adjacent ends of conductors 94 and 96 are inturn soldered together by the joint 98. of fuse link which when heatedby a moderate overloa seversfirst either at the joint 98 or at one orboth ofthe small vconductors 94=and 96. The fusion of these elements ofcourse opens the circuit between the end terminal assemblies 14 and 16and releases the latches 36 and 70. It isvwith reference to i the coronaproduced around the small conductors 94 and 96 that the presentinvention is particularly directed.

We have found that, by'the provision of what is in effect a tubular.resistor of high resistance value which surrounds the small fusiblewires-94 and 96 of the fuse link and which is connected-at itsoppositeends electrically to the end terminals so that it is, electrically in,

- parallel with the fuse link, the corona heretofore present around thefusible element and the undesirable results therefrom-previously pointedout, can be substantially eliminated.

The improved fuse link tube structure, which is best shown in F 2 and 4,preferably includes an internal cylindrical her or other, suitable gasproducing liner 100 extending between the end terminals and which thefuse lmk 10 agasses and a relatively thick cylin- Qo drical body lti2 ofB through elite. or other suitable insulating material formed insurrounding relation to and coextenslve in len with the fiber liner 100.Such a tubular fuse seen to this invention is then provided with layer104 of electrically resistive material having a high 55 value ofresistivity applied to the entire exterior surface of body 102 and anexternal cylinder layer 106 of Bakelite or other suitable insulatingmaterial surrounds the layer 104 to provide a protective insulatingwrapper therefor.

As is shown in Figure 4, the fuse tube extends into the cylindricalaperture 62 of contact casting 60. Electrical contact between casting 60and the resistive layer 104 may be established in any suitable mannerand in the illustrated form is established by the provisions of anextension of the resistive layer 104 over the exterior surface of theend of the wrapper 106 as indicated at 108. The opposite end of fusetube 12 is mounted in casting 26 and electrical connection betweencasting 26 and resistive layer 104 is established in the same manner.

so Since both the fuse link 10 and the cylindrical resistive layer 104are electrically connected to both terminal castings 26 and 60,resistive layer 104 constitutes a cylindrical resistor of highresistance value electrically in parallel with and surrounding the fuselink 10. Resistive layer 104 may be formed of any suitable resistivematerial. Among those found satisfactory are a coatingof finely groundcarbon in varnish of suitable thickness, or a layer of resistor paintsuch as those described in National Bureau of Standards Circular No.468, entitled "Printed Circuit Techniques," at pages 7 to 9. Acylindrical resistor formed of a layer of resistive tape wrapped aroundthe insulating tubular body 102 has been also found to be satisfactoryin practice.

The value of resistance of the layer 104 between the end terminals mustof necessity be a compromise between two design considerations: 1. Afterfuse operation there is a voltage impressed end to end; this must notcause overheating of the resistor or the insulating elements. If suchoverheating does occur, the normal circuit interrupting properties maybe interfered with. 2. During normal operation, the resistor coatingmust carry the surface charging current; the 1R drop due to this currentmust not exceed the critical corona voltage between the link and thetube.

As a specific example of a practical form of the present invention, afuse having a rating of 110,000 volts should have a resistance value ofthe layer 104 between the ends of the fuse of the order of 470 megohms.A fuse of such rating may be provided with a tubular housing having anoutside diameter of two and one-quarter inches, and inside diameter of/8 of an inch, and an overall length of 46 inches. For such a fuse, thatthe potential difference between the fuse link and the adjacent outersurface of the tubular housing is reduced by the presence of theresistive layer 104 to approximately one-fifth of the potentialdifference for a tubular housing of the same dimensions without theresistive layer. This reduction of potential substantially eliminatesthe corona heretofore present around the fusible elements of the fuselink. The elimination or substantial reduction of the corona by thetubular housing of the present invention has extended the life of thefuse links to at least from 4 to 6 times the period of from 3 to 6months heretofore existing and extends the life of the gas producingliner indefinitely in the absence of destruction due to burning utponnormal fuse operation.

The fuse construction the present invention, therefore eliminates thehigh service costs heretofore necessary in air break fuses and adaptssuch air break fuses for use in lieu of the relatively expensive oilcircuit breakers, chemical or liquid type fuses in many situations wherefrequent servicing would be impractical because of either high costs or[undesriable] undesirable service interruptions.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is, therefore, to

be considered in all respects as illustrative and not restrictive, thescope of the invention being indicated by the to be secured by Unitedconducting terminal at each end of said tube adapting it has been foundsaid tube ends for electrical connection to a pair of spaced lineterminals; a [fibre] sleeve closely fitting said axial bore and adaptedupon fuse operation to emit arc extinguishing gases; a replaceablefusible link extending through said [fibre] sleeve and having a smallfusible element interposed between relatively large flexible endterminal connected conductors adapted to be connected to said spacedline terminals to provide a normal current carrying connectiontherebetween; a resistor layer of high electrical resistivitysurrounding said tube body and extending into said sleeve-likeconducting terminals to electrically connect said sleeve-liketerminals-for reducing the potential difference between the fusible linkand the exterior surface of said insulating tube to a degree suflicientto substantially prevent corona troubles along the surface of saidfusible link within said insulating tube body; and an outer layer ofsuitable insulating material surrounding said resistive layer betweensaid sleeve-like tube terminals adapted to protect said resistive layerfrom exposure tothe deleterious effects of the surrounding atmosphere.

2. A fuse tube structure according to claim 1 wherein said resistivelayer comprises a resistive tape wrapped around said insulating tubebody.

3. A fuse tube structure according to claim 1 wherein the voltageresistance relationship between the fuse element and the end to endresistance of the resistive coating is proportional to the ratio of110,000 volts to 470 megohms.

References Cited in the file of this patent or the original patentUNITED STATES PATENTS

